Several assistive devices have improved the metabolic cost of locomotion since these pioneering studies [1]}. Most of these devices assist the hip or the ankle joints, with the exception of an untethered active knee exoskeleton in [2]}, which has been reported to reduce the metabolic burden of incline walking by 4.2% while carrying loads. Among these devices, tethered exoskeletons have been reported to improve metabolic burden by 5.4%–17.4%, while untethered devices reduced the metabolic cost by 3.3%–19.8%. Hip exoskeletons showed superior performance compared to ankle devices: the metabolic cost improvements of tethered and untethered hip devices were reported as 17.4% and 19.8%, respectively, while tethered and untethered ankle exoskeleton improved the walking efficiency by 12% and 11%. All devices that have been reported to improve the metabolic cost of human running were developed for the hip joint: passive hip devices reduced the metabolic burden by 6.4%–8%, while active hip devices reduced metabolic cost by 3.9%–5.4%, respectively [1]}. In addition to assisting healthy subjects, some assistive devices have been successfully employed in improving the walking economy of elderly [4]}, [5]} and patients with gait abnormality [6]}. For instance, in [6]}, a 32% \(\pm \)  9% metabolic cost reduction is reported for post-stroke patients during walking using a tethered exosuit. Readers are referred to comprehensive survey papers for the details of these studies [1]}, [9]}, [10]}.
